A conventional apparatus for driving a laser diode array comprises laser diodes mounted on a common board (non-monolithic type), drive circuits for driving the laser diodes, and a control circuit for controlling the drive circuits by detecting light output of the laser diodes. In one type of the conventional laser diode driving apparatus, scramblers each consisting of an encoder and decoder are provided for each channel to scramble light signals.
In operation, the light outputs are detected to control the drive circuits by the control circuit. In the operation, the scrambler provides a mark ratio of 50% for light signals, so that light output power and threshold values of the laser diodes are compensated.
Such compensation is carried out to cope with the phenomenon in which the light emission of the laser diodes becomes instable due to the non-linearity of the laser diodes, when the laser diodes are turned on after the turning-off state of more than a predetermined time, and vise versa.
In the conventional apparatus for driving a laser diode array, however, there is a disadvantage in that the light outputs of the laser diodes must be detected in the whole channel, because the laser diodes do not have the same property in regard to light output power and threshold value. As a result, the size and the cost of the apparatus are increased.